1. Field of the Invention
The present invention relates to an angle measuring method and an angle measuring system, which can be suitably used in a technical field that requires accurate measurement of the rotation angle of a rotor.
2. Description of the Related Art
In order to accurately measure indexing accuracy of a rotor in a machine tool or the like, an angle measuring method using a polygon mirror and an autocollimator (hereinafter referred to as a “polygon mirror method”) or an angle measuring method using a Hirth coupling and a laser interferometer (hereinafter referred to as a “Hirth coupling method”) has conventionally been performed.
The polygon mirror method includes measuring a difference between the rotation angle of an object to be measured on which a polygon mirror is mounted and the angle of the polygon mirror by a high-accuracy autocollimator.
The Hirth coupling method includes rotating an object to be measured to which a Hirth coupling is attached to be a predetermined target angular displacement, counter-rotating the Hirth coupling by an amount corresponding to the target angular displacement after decoupling the Hirth coupling, and comparing the sum of the counter-angular displacement of the Hirth coupling and an angular displacement from a reference position which is measured by a laser interferometer with the target angular displacement of the object to be measured (Japanese National Publication of International Patent Application No. 1994-502727).